/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.runners.core.construction.graph;



import com.bff.gaia.unified.vendor.guava.com.google.common.collect.ImmutableList;

import com.bff.gaia.unified.vendor.guava.com.google.common.collect.ImmutableSet;

import com.bff.gaia.unified.vendor.guava.com.google.common.collect.Maps;

import com.bff.gaia.unified.vendor.guava.com.google.common.collect.Ordering;

import com.bff.gaia.unified.vendor.guava.com.google.common.graph.*;



import java.util.*;

import java.util.Map.Entry;

import java.util.function.Function;



import static com.bff.gaia.unified.vendor.guava.com.google.common.base.Preconditions.checkArgument;

import static com.bff.gaia.unified.vendor.guava.com.google.common.base.Preconditions.checkNotNull;



/** Static utility methods for {@link Network} instances that are directed. */

public class Networks {

  /**

   * An abstract class that can be extended to apply a function in a type safe manner.

   *

   * <p>Applies {@link #typedApply} to all instances of {@code type}. Otherwise returns the existing

   * {@code Node} unmodified.

   */

  public abstract static class TypeSafeNodeFunction<NodeT, T extends NodeT>

      implements Function<NodeT, NodeT> {

    private final Class<T> type;



    public TypeSafeNodeFunction(Class<T> type) {

      checkNotNull(type);

      this.type = type;

    }



    @SuppressWarnings("unchecked")

    @Override

    public final NodeT apply(NodeT input) {

      if (type.isInstance(input)) {

        return typedApply((T) input);

      }

      return input;

    }



    public abstract NodeT typedApply(T input);

  }



  /**

   * Applies the {@code function} to all nodes within the {@code network}. Replaces any node which

   * is not {@link #equals(Object)} to the original node, maintaining all existing edges between

   * nodes.

   */

  public static <NodeT, EdgeT> void replaceDirectedNetworkNodes(

      MutableNetwork<NodeT, EdgeT> network, Function<NodeT, NodeT> function) {

    checkArgument(network.isDirected(), "Only directed networks are supported, given %s", network);

    checkArgument(

        !network.allowsSelfLoops(),

        "Only networks without self loops are supported, given %s",

        network);



    // A map from the existing node to the replacement node

    Map<NodeT, NodeT> oldNodesToNewNodes = new HashMap<>(network.nodes().size());

    for (NodeT currentNode : network.nodes()) {

      NodeT newNode = function.apply(currentNode);

      // Skip updating the network if the old node is equivalent to the new node

      if (!currentNode.equals(newNode)) {

        oldNodesToNewNodes.put(currentNode, newNode);

      }

    }



    // For each replacement, connect up the existing predecessors and successors to the new node

    // and then remove the old node.

    for (Entry<NodeT, NodeT> entry : oldNodesToNewNodes.entrySet()) {

      NodeT oldNode = entry.getKey();

      NodeT newNode = entry.getValue();

      network.addNode(newNode);

      for (NodeT predecessor : ImmutableSet.copyOf(network.predecessors(oldNode))) {

        for (EdgeT edge : ImmutableSet.copyOf(network.edgesConnecting(predecessor, oldNode))) {

          network.removeEdge(edge);

          network.addEdge(predecessor, newNode, edge);

        }

      }

      for (NodeT successor : ImmutableSet.copyOf(network.successors(oldNode))) {

        for (EdgeT edge : ImmutableSet.copyOf(network.edgesConnecting(oldNode, successor))) {

          network.removeEdge(edge);

          network.addEdge(newNode, successor, edge);

        }

      }

      network.removeNode(oldNode);

    }

  }



  /**

   * Returns the set of nodes that are reachable from {@code startNodes} up to and including {@code

   * endNodes}. Node B is defined as reachable from node A if there exists a path (a sequence of

   * adjacent outgoing edges) starting at node A and ending at node B which does not pass through

   * any node in {@code endNodes}. Note that a node is always reachable from itself via a

   * zero-length path.

   *

   * <p>This is a "snapshot" based on the current topology of the {@code network}, rather than a

   * live view of the set of nodes reachable from {@code node}. In other words, the returned {@link

   * Set} will not be updated after modifications to the {@code network}.

   */

  public static <NodeT, EdgeT> Set<NodeT> reachableNodes(

      Network<NodeT, EdgeT> network, Set<NodeT> startNodes, Set<NodeT> endNodes) {

    Set<NodeT> visitedNodes = new HashSet<>();

    Queue<NodeT> queuedNodes = new ArrayDeque<>();

    queuedNodes.addAll(startNodes);

    // Perform a breadth-first traversal rooted at the input node.

    while (!queuedNodes.isEmpty()) {

      NodeT currentNode = queuedNodes.remove();

      // If we have already visited this node or it is a terminal node than do not add any

      // successors.

      if (!visitedNodes.add(currentNode) || endNodes.contains(currentNode)) {

        continue;

      }

      queuedNodes.addAll(network.successors(currentNode));

    }

    return visitedNodes;

  }



  /**

   * Return a set of nodes in sorted topological order.

   *

   * <p>Note that back edges within directed graphs are "broken" returning a topological order for a

   * directed acyclic network which approximates the original network.

   *

   * <p>Nodes will be considered in the order specified by the {@link Network Network's} {@link

   * Network#nodeOrder()}.

   */

  public static <NodeT> Iterable<NodeT> topologicalOrder(Network<NodeT, ?> network) {

    return computeTopologicalOrder(Graphs.copyOf(network));

  }



  /**

   * Return a set of nodes in sorted topological order.

   *

   * <p>Note that back edges within directed graphs are "broken" returning a topological order for a

   * directed acyclic network which approximates the original network.

   *

   * <p>Nodes will be considered in the order specified by the {@link

   * ElementOrder#sorted(Comparator) sorted ElementOrder} created with the provided comparator.

   */

  public static <NodeT, EdgeT> Iterable<NodeT> topologicalOrder(

      Network<NodeT, EdgeT> network, Comparator<NodeT> nodeOrder) {

    // Copy the characteristics of the network to ensure that the result network can represent the

    // original network, just with the provided suborder

    MutableNetwork<NodeT, EdgeT> orderedNetwork =

        NetworkBuilder.from(network).nodeOrder(ElementOrder.sorted(nodeOrder)).build();

    for (NodeT node : network.nodes()) {

      orderedNetwork.addNode(node);

    }

    for (EdgeT edge : network.edges()) {

      EndpointPair<NodeT> incident = network.incidentNodes(edge);

      orderedNetwork.addEdge(incident.source(), incident.target(), edge);

    }

    return computeTopologicalOrder(orderedNetwork);

  }



  /**

   * Compute the topological order for a {@link Network}.

   *

   * <p>Nodes must be considered in the order specified by the {@link Network Network's} {@link

   * Network#nodeOrder()}. This ensures that any two Networks with the same nodes and node orders

   * produce the same result.

   */

  private static <NodeT> Iterable<NodeT> computeTopologicalOrder(MutableNetwork<NodeT, ?> network) {

    // TODO: (github/guava/2641) Upgrade Guava and remove this method if topological sorting becomes

    // supported externally or remove this comment if its not going to be supported externally.



    checkArgument(network.isDirected(), "Only directed networks are supported, given %s", network);

    checkArgument(

        !network.allowsSelfLoops(),

        "Only networks without self loops are supported, given %s",

        network);



    // Uses the following algorithm:

    //    A FAST & EFFECTIVE HEURISTIC FOR THE FEEDBACK ARC SET PROBLEM

    //    Peter Eades, Xuemin Lin, W. F. Smyth

    // https://pdfs.semanticscholar.org/c7ed/d9acce96ca357876540e19664eb9d976637f.pdf

    //

    // The only edges that are ignored by the algorithm are back edges.

    // The algorithm (while there are still nodes in the graph):

    //   1) Removes all sinks from the graph adding them to the beginning of "s2". Continue to do

    // this till there

    //      are no more sinks.

    //   2) Removes all source from the graph adding them to the end of "s1". Continue to do this

    // till there

    //      are no more sources.

    //   3) Remote a single node with the highest delta within the graph and add it to the end of

    // "s1".

    //

    // The topological order is then the s1 concatenated with s2.



    Deque<NodeT> s1 = new ArrayDeque<>();

    Deque<NodeT> s2 = new ArrayDeque<>();



    Ordering<NodeT> maximumOrdering =

        new Ordering<NodeT>() {

          @Override

          public int compare(NodeT t0, NodeT t1) {

            return (network.outDegree(t0) - network.inDegree(t0))

                - (network.outDegree(t1) - network.inDegree(t1));

          }

        };



    while (!network.nodes().isEmpty()) {

      boolean nodeRemoved;

      do {

        nodeRemoved = false;

        for (NodeT possibleSink : ImmutableList.copyOf(network.nodes())) {

          if (network.outDegree(possibleSink) == 0) {

            network.removeNode(possibleSink);

            s2.addFirst(possibleSink);

            nodeRemoved = true;

          }

        }

      } while (nodeRemoved);



      do {

        nodeRemoved = false;

        for (NodeT possibleSource : ImmutableList.copyOf(network.nodes())) {

          if (network.inDegree(possibleSource) == 0) {

            network.removeNode(possibleSource);

            s1.addLast(possibleSource);

            nodeRemoved = true;

          }

        }

      } while (nodeRemoved);



      if (!network.nodes().isEmpty()) {

        NodeT maximum = maximumOrdering.max(network.nodes());

        network.removeNode(maximum);

        s1.addLast(maximum);

      }

    }



    return ImmutableList.<NodeT>builder().addAll(s1).addAll(s2).build();

  }



  public static <NodeT, EdgeT> String toDot(Network<NodeT, EdgeT> network) {

    StringBuilder builder = new StringBuilder();

    builder.append(String.format("digraph network {%n"));

    Map<NodeT, String> nodeName = Maps.newIdentityHashMap();

    network.nodes().forEach(node -> nodeName.put(node, "n" + nodeName.size()));

    for (Entry<NodeT, String> nodeEntry : nodeName.entrySet()) {

      builder.append(

          String.format(

              "  %s [fontname=\"Courier New\" label=\"%s\"];%n",

              nodeEntry.getValue(), escapeDot(nodeEntry.getKey().toString())));

    }

    for (EdgeT edge : network.edges()) {

      EndpointPair<NodeT> endpoints = network.incidentNodes(edge);

      builder.append(

          String.format(

              "  %s -> %s [fontname=\"Courier New\" label=\"%s\"];%n",

              nodeName.get(endpoints.source()),

              nodeName.get(endpoints.target()),

              escapeDot(edge.toString())));

    }

    builder.append("}");

    return builder.toString();

  }



  private static String escapeDot(String s) {

    return s.replace("\\", "\\\\")

        .replace("\"", "\\\"")

        // http://www.graphviz.org/doc/info/attrs.html#k:escString

        // The escape sequences "\n", "\l" and "\r" divide the label into lines, centered,

        // left-justified, and right-justified, respectively.

        .replace("\n", "\\l");

  }



  /**

   * Returns a list of all distinct paths from roots of the network to leaves. The list can be in

   * arbitrary orders and can contain duplicate paths if there are multiple edges from two nodes.

   */

  public static <NodeT, EdgeT> List<List<NodeT>> allPathsFromRootsToLeaves(

      Network<NodeT, EdgeT> network) {

    ArrayDeque<List<NodeT>> paths = new ArrayDeque<>();

    // Populate the list with all roots

    for (NodeT node : network.nodes()) {

      if (network.inDegree(node) == 0) {

        paths.add(ImmutableList.of(node));

      }

    }



    List<List<NodeT>> distinctPathsFromRootsToLeaves = new ArrayList<>();

    while (!paths.isEmpty()) {

      List<NodeT> path = paths.removeFirst();

      NodeT lastNode = path.get(path.size() - 1);

      if (network.outDegree(lastNode) == 0) {

        distinctPathsFromRootsToLeaves.add(new ArrayList<>(path));

      } else {

        for (EdgeT edge : network.outEdges(lastNode)) {

          paths.addFirst(

              ImmutableList.<NodeT>builder()

                  .addAll(path)

                  .add(network.incidentNodes(edge).target())

                  .build());

        }

      }

    }

    return distinctPathsFromRootsToLeaves;

  }



  // Hide visibility to prevent instantiation

  private Networks() {}

}